In order to suppress AC input line harmonics, a power factor correction (PFC) converter is used, such as disclosed in Patent Document 1, for example. The PFC converter is a circuit for correcting power factor by approximating the waveform and phase of input current to the input voltage waveform. FIG. 25 shows a typical boost PFC converter. Further, FIG. 26 shows two PFC converter sections (PFC1 and PFC2) connected in parallel to each other.
The circuits shown in FIGS. 25 and 26 include a diode bridge Db for full-wave rectifying AC input voltage Vi from a commercial power supply E as input power supply, and a first converter section PFC1 being applied with rectification output from the diode bridge Db (rectifier). The first converter section PFC1 includes a series circuit of a first inductor L1 and a first switching element S1, connected between the output terminals of the diode bridge Db, and a first rectification element D1 as a diode with one end (anode) connected to the connecting point of the inductor L1 and the switching element S1. Also, a smoothing capacitor Co is connected between the output terminals of the converter section PFC1, i.e., between the other end (cathode) of the rectification element D1 and the connecting point of the diode bridge Db and the switching element S1. Then, output terminals +V, −V for generating DC output voltage Vo are connected across the smoothing capacitor Co.
The circuit configuration described above is common to FIGS. 25 and 26. In addition, in FIG. 26, the first converter section PFC1 and a second converter section PFC2 are connected in parallel between the diode bridge Db and the smoothing capacitor Co. As shown, the converter section PFC2 includes a series circuit of a second inductor L2 and a second switching element S2, connected between the output terminals of the diode bridge Db, and a second rectification element D2 as a diode with one end (anode) connected to the connecting point of the inductor L2 and the switching element S2. The smoothing capacitor Co is also connected between the output terminals of the converter section PFC2.
As shown in FIG. 26, the power capacity of the overall PFC converter can be increased by increasing the number of the converter sections PFC1, PFC2 and so on connected in parallel. Also, the ripple in input current and output current can be reduced by causing a phase shift between the converter sections PFC1 and PFC2, and then switching-driving the switching elements S1 and S2 of the converter sections PFC1 and PFC2, respectively.